Direct current motor having a threepole armature and an annular twopole magnet



`Ilan. 30, 1968 H. WULLKOPF DIRECT CURRENT MOTOR HAVING A THREE-FOL ARMATURE AND AN ANNULAR TWO-POLE MAGNET Original Filed Sept. 2l, 1964 2 Sheets-Sheet 2 .QQ s@ Q "SQ" /912 zj, Flg.3 11

T/ W /ob Q '6) b B A W) Fig l l g 0 9o"4 160 270BY 360 INVENTOR. HELLMUTH wuLLKoPF AGENT 3,366,811 DIRECT CURRENT MTOR HAVING A THREE- POLE ARMATURE AND AN ANNULAR TWG- ILE MAGNET Hellmuth Wulikopf, Hamburg-Gross, Flottbek, Germany, assigner to North American Philips Company, Inc., New York NY., a corporation of Delaware Original application Sept. 21, 1964, Ser. No. 397,733, now Patent No. 3,317,872, dated May 2, 1967. Divided and this application Sept. 14, 1966, Ser. No. 594,304

4 Claims. (Cl. S10-15d) Ansrnncr or rim msctosonn A direct-current motor with high starting and output torques having a three-pole armature and a two-pole annular magnet magnetized peripherally and having a radial component of induction including only the fundamental and third harmonic of a sinusoidal wave.

The invention relates to an annular two-pole permanent magnet, particularly to a magnet constituted of barium hexaferrite, for use in direct current motors having three-pole armatures.

This is a division of Ser. No. 397,733, led Sept. 21, 1964, now Patent No. 3,317,872, issued May 2, 1967.

The invention will be described with reference to the accompanying drawing in which:

FIGS. 1 and 2 are diagrammatic sectional views of direct-current motors known in the art,

FIG. 3 is a diagrammatic sectional View of a device for magnetizing a magnet according to the invention; and,

FIG. 4 is a curve showing the variation of magnetic induction about the periphery of the magnet of FIG. 3.

In FIGS. 1 and 2 the DC. motors have annular magnets 1 and 2 respectively which are made of barium hexaferrite and are magnetized radially (FIG. l) and diametrically (FIG. 2). Reference numeral 3 designates an iron short-circuiting plate and reference numeral 4 an armature. The air gap between the permanent magnet 1 or 2 respectively and the armature 4 is designated by 5. In the motor shown in FIGURE 1 the lines of magnetic force 6 pass radially through the magnet I and in the motor shown in FIGURE 2 the lines of magnetic force 7 pass diametrically through the magnet 2.

A specic problem in D.C. motors, particularly small. motors for record players or battery-energized apparatus, in the so-called sticking of the armature when no current is supplied thereto, which sticking occurs preferentially in particular positions determined by the magnetic field and gives rise to irregular running of the motor. Starting of such a motor requires an additional torque. This torque is required to overcome the forces which hold the armature in its preferential position. Apart from the irregular running the sticking positions do not influence the motor when running.

It is known that D.C. motors having diametrical magnetization of the annular magnet have no sticking positions. In such motors the induction around the permanent magnet is truly sinusoidal. In contradistinction thereto, motors having radially magnetized armatures have marked sticking positions. On the other hand, with otherwise equal dimensions of a motor radial magnetization enables an armature flux to be produced which exceeds the armatureflux obtainable with diametrical magnetization by more than 50%. Thus, diametrical magnetization provides motors having no sticking positions and a comparatively small armature tlux and hence a small output torque, whereas radial magnetization provides motors having an armature flux which is greater by more than 50% Sdl l Patented Jan. so, lees According to the invention a motor having no or substantially negligible sticking positions and yet a large armature ilux is obtainable by providing the permanent mag- B.=CB,. (1.14 sin @+0.23 sin 3,0)

In this formula Br is the remanent induction of the material of the magnet and C is a constant dependent on the geometrical proportions of the motor.

According to the invention, to achieve a maximum armature iiux the amplitude ratio between the fundamental Wave and the third harmonic must be at least 2:1 but preferably approximately 5:1.

A motor having an annular magnet magnetized in accordance with the invention has substantially no sticking positions and produces an armature ilux which is about intermediate between armature iiux of a radially magnetized annular magnet and the armature ux of a diametrically magnetized annular magnet. Compared with a motor having a diametrically magnetized permanent magnet and hence no sticking positions, an annular magnet magnetized in accordance with the invention provides an increase in the armature iiux of about 20% to 25% If the magnetic induction over the inner cylindrical surface is measured, for example, by means of a Hall probe, a variation is found as Shown in FIGURE 4 by curve a drawn as a heavy full line. This curve a is constituted by a sinusoidal fundamental wave b and its third harmonic c.

An annular magnet may be provided with a magnetization according to curve a in a variety of manners.

A method of magnetizing a permanent magnet in accordance with the invention is characterized in that the annular permanent magnet is simultaneously exposed to a diametrical homogeneous magnetic field and two circular magnetic fields which are produced in this case by two conductors which have opposite current directions and lie in a plane passing through the axis of the annular magnet at right angles to the homogeneous field and are arranged both diametrically and parallel to this axis.

It may be of advantage to arrange a soft-iron core in the permanent annular magnet during the magnetizing process.

FIGURE 3 shows an arrangement by means of which an annular magnet may be magnetized in accordance with the invention.

An annular magnet 8 made of barium hexaferrite (nal) is subjected to a diametrical homogeneous magnetic eld 9 produced by two series-connected annular coils 10a and 10b having the same current direction. The annular coils 10 are shown schematically only since such an arrangement is known. Two circular magnetic elds 11 and 12 produced by two conductors 13 and 14 arranged externally of the permanent magnet 8 parallel to its axis are superposed on the homogeneous diametrical .magnetic field 9. The coils l0 and the conductors 13 and 14 are preferably connected in series and advantageously consist of a single length of wire. The superposition of the magnetic iields 9, 11 and 12 produces in the annular magnet 8 a resultant magnetization the variation of the lines of force of which is substantially intermediate the variation with radial magnetization and that with diametrical magnetization when the magnetizing coils are connected in the aforedescribed manner and are traversed, for example, by a current pulse produced by the discharge of a capacitor.

'sa d Along the circumference of the magnet the resultant magnetization has an induction variation which corresponds at least approximately to the curve n of FIGURE 4. In order to cause the variation of the induction to approximate still closer to the ideal shape a soft-iron core l5 may be arranged in the permanent annular magnet 8 during the magnetizing process. The annular magnet need not be in one piece but may comprise a plurality of ring segments.

What is claimed is: Y

1. A direct-current motor comprising a three-pole armature and an annular two-pole permanent magnet operatively coupled to said armature magneti/Zed about the periphery thereof and 4having a radial component of induction which comprises substantially only a sinusoidal fundamental wave and the third harmonic thereof, said motor having both high starting and output torques.

2. A direct-current motor as claimed in claim 1, in which the amplitude ratio between the fundamental Wave and the third harmonic is atleast 2:1.

3. A direct-current motor as claimed in claim 2, in which the amplitude ratio between the fundamental Wave and the third harmonic iS 5:1.

4. A direct-current motor as claimed in claim 3, in which the magnet consists essentially of barium hexaferrite.

No references cited.

MILTON O. HlRSHFIELD, Primary Examiner.

15 L. L. SMTH, Assistant Examiner. 

